High-power diode-pumped fiber laser operating at 3 μm

Abstract

A high-power diode-cladding-pumped Ho 3þ -doped fluoride glass fiber laser operating in cascade mode is demonstrated. The 5 I 6 → 5 I 7 and 5 I 7 → 5 I 8 laser transitions produced 0:77 W at a measured slope efficiency of 12.4% and 0:24 W at a measured slope efficiency of 5.2%, respectively. Using a long fiber length, which forced a large threshold for the 5 I 7 → 5 I 8 transition, a wavelength of 3:002 μm was measured at maximum output power, making this system the first watt-level fiber laser operating in the mid-IR. © 2011 Optical Society of America OCIS codes: 140.3510, 140.3480.The burgeoning field of mid-IR photonics requires a variety of pump and probe sources in order to create the integrated optical devices required for the plethora of applications in defense, health, and the environment. The mid-IR region of the spectrum that is relevant to optics and photonics spans 3 to 50 μm [1] and contains most of the signatures relating to biochemicals and other molecular compounds. Traditionally, research into fiber lasers using fluoride glasses operating in the far shortwave region of the spectrum has been driven by requirements in medicine and materials processing; however, as demands develop from mid-IR photonics, pushing the emission wavelength of fiber lasers further into the mid-IR is desirable. To date, the rare earth ions erbium [2], holmium [3], and dysprosium [4] have created the highest output power and efficiency in the far shortwave IR region with the former two ions also generating low power emission in the near mid-IR region albeit at low efficiencies [5][6][7]. A recent report [8] of an all-fiber erbium-doped ZBLAN 2:825 μm fiber laser emitting 20:6 W of single transverse mode output power demonstrates the maturity and utility of fluoride glass fiber lasers for long wavelength emission. This result suggests that fluoride glass fiber lasers could find application as pump sources for mid-IR integrated optics. Holmium-doped fluoride glass fiber lasers operating on the 5 I 6 → 5 I 7 laser transition (see Fig. 1) have shown high efficiency, high power [9], and broad tunability and offer the opportunity, as a result of the longer fluorescence wavelength compared to erbium, to extend the emission from fiber lasers into the mid-IR region while utilizing a diode-pumped format and operation at room temperature.The 5 I 6 → 5 I 7 laser transition of Ho 3þ is potentially selfterminating because the lifetime of the upper laser level is shorter than the lower laser level lifetime [10], see Fig. 1. As a result, high-power holmium-based fluoride glass fiber lasers have used cascade lasing [11] or codoping with Pr 3þ ions [3] in order to depopulate the lower laser level. In this Letter, we demonstrate using direct diode pumping of the upper laser level, cascade lasing of both the 5 I 6 → 5 I 7 and 5 I 7 → 5 I 8 laser transitions. With the use of holmium-only doping so that the lower laser level is not efficiently de-excited and a long fiber length that produces a high threshold for the 5 I 7 → 5 I 8 laser transiti...

Watt-level passively Q-switched heavily Er3+-doped ZBLAN fiber laser with a semiconductor saturable absorber mirror

“…Thanks to commercially available high power laser diode as pumping sources, significant progresses of continuous wave (CW) ZBLAN fiber lasers at 3 μm have been achieved over the past decade123467891011, and the maximum recorded power in excess of 20 W was obtained89. However, some special applications, such as, material processing, micro surgery and nonlinear optical process, require a high pulse energy laser source, and thus Q-switched operation of ZBLAN fiber lasers is highly desired and thereby prior to CW and mode-locking operation12.…”

Mid-infrared fiber lasers at and beyond 35 μm using dual-wavelength pumping

“…Recently, there have been significant advances in fiber laser performance at wavelengths up to 3 μm with 0.77 W CW power achieved at 3 μm [9]. However, the development of fiber lasers operating well beyond 3 μm has lagged considerably [10].…”

Dual wavelength Q-switched cascade laser

“…The free running 5 I 7 → 5 I 8 transition operates at a center wavelength of 2.074 μm and bandwidth of 2 nm which broadens to 5 nm. Note that the emission wavelength of the 5 I 6 → 5 I 7 transition is now longer than the measurements made in [9] which involved a shorter fiber length of 10 m. The longer fiber length in the current demonstration forces a higher threshold for the 5 I 7 → 5 I 8 transition which increases the population in the 5 I 7 manifold and the terminating Stark level for the 5 I 6 → 5 I 7 transition is now higher up the 5 I 7 manifold. Figure 4 shows the pulse widths for the 3 μm and 2.1 μm transitions as a function of repetition rate and launched pump power.…”

“…1. The Ho 3 -doped double clad fiber (FiberLabs, Japan) was identical to the fiber used in our previous free running experiment [9] and had a D-shaped pump core with a diameter of 125 μm across the circular cross-section and a numerical aperture (NA) of 0.50. The fiber had a 10 μm core diameter with an NA of 0.16.…”

“…A recent report of a Watt-level diode-cladding-pumped Ho 3 -doped fluoride cascade fiber laser free running at 3.002 μm [9] demonstrated that Ho 3 -dopedfluoride glass fiber lasers can extend the emission wavelength into the mid-IR. Moreover, the cascade lasing on both the 5 I 6 → 5 I 7 and the 5 I 7 → 5 I 8 laser transitions is a straight forward process not reliant on strong cavity resonances and offers the opportunity for all infrared emission with little visible light generation owing to comparatively reduced levels of pump excited state absorption.…”